Improvement of coercivity and microstructure by internal grain boundary diffusion of SPSed Nd-Fe-B magnet

Abstract

High performance Nd-Fe-B sintered magnets are currently being actively researched for a variety of applications, with the grain boundary diffusion process (GBDP) being widely utilized for increase the coercivity of Nd-Fe-B sintered magnets. The process involves coating the magnet surface with heavy rare earth elements such as Dy and Tb, followed by diffusion along the grain boundary. However, detrimental effects are caused by non-uniform diffusion and grain growth. In this study, high density Nd-Fe-B sintered magnet was fabricated using spark plasma sintering (SPS), and grain growth was effectively suppressed. SPSed magnet were fabricated by mixing Tb and Nd-Fe-B powder at optimal SPS conditions. Through heat treatment, internal grain boundary diffusion was performed, and coercivity was improved. The magnetic properties and microstructure of SPSed magnet treated with internal grain boundary diffusion were investigated.